排序方式： 共有10条查询结果，搜索用时 62 毫秒
1
1.
Melkamu Meseret Alemu 《资源与生态学报(英文版)》2019,10(1):77-85
Analysis of the nexus between vegetation dynamics and climatic parameters like surface temperature is essential in environmental and ecological studies and for monitoring of the natural resources. This study explored the spatio-temporal distribution of land surface temperature (LST) and Normalized Difference Vegetation Index (NDVI) and the relationship between them in the Andassa watershed from 1986 to 2016 periods using Landsat data. Monthly average air temperature data of three meteorological sites were used for validating the results. The findings of the study showed that the LST of the Andassa watershed has increased during the study periods. Overall, average LST has been rising with an increasing rate of 0.081°C per year. Other results of this study also showed that there has been a dynamic change in vegetation cover of the watershed in all seasons. There was also a negative correlation between LST and NDVI in all the studied years. From this study we can understand that there has been degradation of vegetation and intensification of LST from 1986 to 2016. 相似文献
2.
This study is aimed at demonstrating the feasibility of the large scale LAI inversion algorithms using red and near infrared reflectance obtained from high resolution satellite imagery. Radiances in digital counts were obtained in 10 m resolution acquired on cloud free day of August 23, 2007, by the SPOT 5 high resolution geometric (HRG) instrument on mostly temperate hardwood forest located in the Great Lakes – St. Lawrence forest in Southern Quebec. Normalized difference vegetation index (NDVI), scaled difference vegetation index (SDVI) and modified soil-adjusted vegetation index (MSAVI) were applied to calculate gap fractions. LAI was inverted from the gap fraction using the common Beer–Lambert's law of light extinction under forest canopy. The robustness of the algorithm was evaluated using the ground-based LAI measurements and by applying the methods for the independently simulated reflectance data using PROSPECT + SAIL coupled radiative transfer models. Furthermore, the high resolution LAI was compared with MODIS LAI product. The effects of atmospheric corrections and scales were investigated for all of the LAI retrieval methods. NDVI was found to be not suitable index for large scale LAI inversion due to the sensitivity to scale and atmospheric effects. SDVI was virtually scale and atmospheric correction invariant. MSAVI was also scale invariant. Considering all sensitivity analysis, MSAVI performed best followed by SDVI for robust LAI inversion from high resolution imagery. 相似文献
3.
Melkamu Meseret Alemu 《资源与生态学报(英文版)》2019,(1)
本文分析了植被动态与地表温度等气候参数之间的关系,对环境和生态研究以及自然资源监测至关重要。本文首先利用Landsat数据探讨了1986年至2016年期间安达萨河流域地表温度(LST)和归一化植被指数(NDVI)的时空分布以及它们之间的关系,三个气象站点的月平均气温数据用于验证结果。该研究的结果表明,Andassa流域的LST在研究期间有所增加。总体而言,平均LST一直在上升,年增长率为0.081℃yr~(-1)。该研究结果还表明,所有季节的流域植被覆盖都发生了变化。在所有研究年份中,LST和NDVI之间存在负相关;从1986年到2016年,研究区植被具有退化趋势,地表温度有所升高。 相似文献
4.
V. Kazmin Alemu Shifferaw Tilahun Balcha 《International Journal of Earth Sciences》1978,67(2):531-546
In the Ethiopian Precambrian three complexes are recognized. The Lower Complex formed of high grade gneisses represents older (older than 2500 m. y.) cratonic basement. The Middle Complex (clastic metasediments) is presumably the Lower to Middle Proterozoic platform cover. The Upper Complex consists of low-grade rocks in following succession: ophiolitic rocks, andesitic metavolcanics and associated metasediments, clastic and to less extent carbonate sediments. Rifting of older basement at the beginning of Upper Proterozoic created northeasterly trending zones with oceanic crust branching from the Red Sea fold belt and grading southwards (in the Mozambique belt) into the zones of continental rifting. Closing of these rift zones terminated 1000 m. y. ago and was accompanied by subduction of oceanic crust which gave rise to island arc type volcanism. Continental collision resulted in crustal thickening and produced two stages of metamorphism: metamorphism of collision (around 1000 m. y. or earlier) and metamorphism of radioactive heating (younger than 1000 or 800 m. y.). The collision was oblique, so the significant transcurrent motion occurred in the Red Sea and the Mozambique belts.
Zusammenfassung Im Präkambrium Äthiopiens lassen sich drei Einheiten unterscheiden. Die unterste Einheit, bestehend aus hochgradig metamorphen Gneisen, ist ein älterer (älter als 2,5 Mrd. Jahre) kratonischer Sockel. Der mittlere Komplex (klastische Metasedimente) stellt wahrscheinlich die altbis mittelproterozoische Plattform-Sedimentbedeckung dar. Die obere Einheit besteht aus niedrigmetamorphen Gesteinen: Ophiolithe, andesitische Metavulkanite und damit verbundene Metasedimente, sowie klastische und untergeordnet karbonatische Ablagerungen. Das Auseinanderreißen des älteren Sockels zu Beginn des Jungproterozoikums bewirkte in nordöstliche Richtung verlaufende Zonen mit ozeanischer Kruste, die vom Faltengürtel des Roten Meeres abbiegen und sich südwärts (zum Mozambique-Gürtel hin) in das kontinentale Riftsystem eingliedern. Dei Abschluß dieser Riftsysteme endete vor 1 Mrd. Jahren, begleitet von einer Subduktion ozeanischer Kruste, die mit Vulkanismus vom Typ der Inselbögen verbunden war. Die Kollision kontinentaler Platten verursachte Krustenverdickungen und erzeugte zwei Stadien der Metamorphose: Kollisions-Metamorphose (vor ca. 1 Mrd. Jahren oder früher) und Metamorphose durch radioaktive Aufheizung (jünger als 1 oder 0,8 Mrd. Jahre). Die Kollision verlief schräg, so daß die signifikanten Querbewegungen im Roten-Meerund Mozambique-Gürtel erfolgten.
Résumé On peut reconnaître trois complexes dans le Précambrien de l'Ethiopie. Le complexe inférieur, formé de gneiss de degré de métamorphisme élevé, représente le socle cratonique le plus ancien (plus vieux que 2500 M.). Le complexe moyen (des métasédiments détritiques) est présumé être une couverture de plateforme du Protérozoïque inférieur à moyen. Le complexe supérieur consiste en roches peu métamorphiques se succédant comme suit: roches ophiolithiques, métavolcanites andésitiques avec sédiments associés, sédiments clastiques et en moindre proportion des sédiments carbonatés. La fracturation du vieux socle au debut du Protérozoïque supérieur créa des zones d'effondrement de direction nord-est, avec croûte océanique, branchées sur la ceinture plissé de la Mer Rouge, et passant vers le sud (dans la ceinture du Mozambique) à une zone de fracturation continentale. La fermeture de cette zone d'affaissement se termina il y a quelque 1000 M., et fut accompagnée par une subduction de la croûte océanique qui donna naissance à un volcanisme du type guirlande insulaire. La collision continentale entraîna un épaississement crustal et produisit deux phases de métamorphisme: métamorphisme de collision (environ 1000 M. ou plus tôt) et métamorphisme par réchauffement radioactif (plus récent que 1000 M. ou 800 M.). La collision se fit obliquement, produisant ainsi un mouvement transcurrent important dans les ceintures de la Mer Rouge et du Mozambique.
. , ( 2500 . .), . ( ) , , - . (): , , , , . - . , , . 100 . . . : ( 1000 . . ) ( 1000 800 . .). , .相似文献
5.
6.
Determinants of farmers’ choice of adaptation methods to climate change in the Nile Basin of Ethiopia 总被引：6，自引：0，他引：6
Temesgen Tadesse Deressa Rashid M. Hassan Claudia Ringler Tekie Alemu Mahmud Yesuf 《Global Environmental Change》2009,19(2):248-255
This study identifies the major methods used by farmers to adapt to climate change in the Nile Basin of Ethiopia, the factors that affect their choice of method, and the barriers to adaptation. The methods identified include use of different crop varieties, tree planting, soil conservation, early and late planting, and irrigation. Results from the discrete choice model employed indicate that the level of education, gender, age, and wealth of the head of household; access to extension and credit; information on climate, social capital, agroecological settings, and temperature all influence farmers’ choices. The main barriers include lack of information on adaptation methods and financial constraints. 相似文献
7.
Binyam L. Alemu Eyvind Aker Magnus Soldal Øistein Johnsen Per Aagaard 《Geophysical Prospecting》2013,61(1):235-250
The effect of sub‐core scale heterogeneity on fluid distribution pattern, and the electrical and acoustic properties of a typical reservoir rock was studied by performing drainage and imbibition flooding tests with CO2 and brine in a laboratory. Moderately layered Rothbach sandstone was used as a test specimen. Two core samples were drilled; one perpendicular and the other parallel to the layering to allow injection of fluids along and normal to the bedding plane. During the test 3D images of fluid distribution and saturation levels were mapped by an industrial X‐ray CT‐scanner together with simultaneous measurement of electrical resistivity, ultrasonic velocities as well as amplitudes. The results showed how the layering and the flooding direction influenced the fluid distribution pattern and the saturation level of the fluids. For a given fluid saturation level, the measured changes in the acoustic and electrical parameters were affected by both the fluid distribution pattern and the layering orientation relative to the measurement direction. The P‐wave amplitude and the electrical resistivity were more sensitive to small changes in the fluid distribution patterns than the P‐wave velocity. The change in amplitude was the most affected by the orientation of the layering and the resulting fluid distribution patterns. In some instances the change due to the fluid distribution pattern was higher than the variation caused by the change in CO2 saturation. As a result the Gassmann relation based on ‘uniform' or ‘patchy' saturation pattern was not suitable to predict the P‐wave velocity variation. Overall, the results demonstrate the importance of core‐imaging to improve our understanding of fluid distribution patterns and the associated effects on measured rock‐physics properties. 相似文献
8.
Binyam L. Alemu Per Aagaard Ingrid Anne Munz Elin Skurtveit 《Applied Geochemistry》2011,26(12):1975-1989
Crushed rock from two caprock samples, a carbonate-rich shale and a clay-rich shale, were reacted with a mixture of brine and supercritical CO2 (CO2–brine) in a laboratory batch reactor, at different temperature and pressure conditions. The samples were cored from a proposed underground CO2 storage site near the town of Longyearbyen in Svalbard. The reacting fluid was a mixture of 1 M NaCl solution and CO2 (110 bar) and the water/rock ratio was 20:1. Carbon dioxide was injected into the reactors after the solution had been bubbled with N2, in order to mimic O2-depleted natural storage conditions. A control reaction was also run on the clay-rich shale sample, where the crushed rock was reacted with brine (CO2-free brine) at the same experimental conditions. A total of 8 batch reaction experiments were run at temperatures ranging from 80 to 250 °C and total pressures of 110 bar (∼40 bar for the control experiment). The experiments lasted 1–5 weeks.Fluid analysis showed that the aqueous concentration of major elements (i.e. Ca, Mg, Fe, K, Al) and SiO2 increased in all experiments. Release rates of Fe and SiO2 were more pronounced in solutions reacted with CO2–brine as compared to those reacted with CO2-free brine. For samples reacted with the CO2–brine, lower temperature reactions (80 °C) released much more Fe and SiO2 than higher temperature reactions (150–250 °C). Analysis by SEM and XRD of reacted solids also revealed changes in mineralogical compositions. The carbonate-rich shale was more reactive at 250 °C, as revealed by the dissolution of plagioclase and clay minerals (illite and chlorite), dissolution and re-precipitation of carbonates, and the formation of smectite. Carbon dioxide was also permanently sequestered as calcite in the same sample. The clay-rich shale reacted with CO2–brine did not show major mineralogical alteration. However, a significant amount of analcime was formed in the clay-rich shale reacted with CO2-free brine; while no trace of analcime was observed in either of the samples reacted with CO2–brine. 相似文献
9.
In April and May 1989 the satellite Global Positioning System (GPS) was employed in the establishment of three deformation networks in the Ethiopian Rift Valley. The net E1 consists of 6 points of about 100–270 km interdistances, with two points located on each of the African and the Somalian plate and two points down in the rift. In addition two separate GPS traverses were established: one (E2) runs across the rift, and one (E3) runs about 500 km along the rift.The remeasurement of a 175 km long baseline included in two subcampaigns indicates a repeatability of the GPS observations of the order of 1×10−7 and 3×10−7 for slope distance and ellipsoidal height, respectively.Along the E2 traverse GPS/trigonometric levelled geoid undulations and gravimetric geoid undulations agree well, while the discrepancy along the E3 traverse needs further analysis. 相似文献
10.
Fatemeh Jalayer Raffaele De Risi Francesco De Paola Maurizio Giugni Gaetano Manfredi Paolo Gasparini Maria Elena Topa Nebyou Yonas Kumelachew Yeshitela Alemu Nebebe Gina Cavan Sarah Lindley Andreas Printz Florian Renner 《Natural Hazards》2014,73(2):975-1001
Identifying urban flooding risk hotspots is one of the first steps in an integrated methodology for urban flood risk assessment and mitigation. This work employs three GIS-based frameworks for identifying urban flooding risk hotspots for residential buildings and urban corridors. This is done by overlaying a map of potentially flood-prone areas [estimated through the topographic wetness index (TWI)], a map of residential areas and urban corridors [extracted from a city-wide assessment of urban morphology types (UMT)], and a geo-spatial census dataset. A maximum likelihood method (MLE) is employed for estimating the threshold used for identifying the flood-prone areas (the TWI threshold) based on the inundation profiles calculated for various return periods within a given spatial window. Furthermore, Bayesian parameter estimation is employed in order to estimate the TWI threshold based on inundation profiles calculated for more than one spatial window. For different statistics of the TWI threshold (e.g. MLE estimate, 16th percentile, 50th percentile), the map of the potentially flood-prone areas is overlaid with the map of urban morphology units, identified as residential and urban corridors, in order to delineate the urban hotspots for both UMT. Moreover, information related to population density is integrated by overlaying geo-spatial census datasets in order to estimate the number of people affected by flooding. Differences in exposure characteristics have been assessed for a range of different residential types. As a demonstration, urban flooding risk hotspots are delineated for different percentiles of the TWI value for the city of Addis Ababa, Ethiopia. 相似文献
1